26-3 Cnidarians - Hamilton Local Schools

26-3 CnidariansSlide1 of 47Copyright Pearson Prentice Hall

26-3 CnidariansWhat Is a Cnidarian?What is a cnidarian?Slide2 of 47Copyright Pearson Prentice Hall

26-3 CnidariansWhat Is a Cnidarian?What Is a Cnidarian?Cnidarians are soft-bodied, carnivorousanimals that have stinging tentaclesarranged in circles around their mouths.They are the simplest animals to havebody symmetry and specialized tissues.Slide3 of 47Copyright Pearson Prentice Hall

26-3 CnidariansWhat Is a Cnidarian?Cnidarians get their name from thecnidocytes, or stinging cells, located alongtheir tentacles.Cnidarians use cnidocytes for defense and tocapture prey.Slide4 of 47Copyright Pearson Prentice Hall

26-3 CnidariansWhat Is a Cnidarian?Within each cnidocyteis a nematocyst—apoison-filled, stingingstructure that containsa tightly coiled dart.TriggerFilamentNematocyteBarbFilamentSlide5 of 47Copyright Pearson Prentice Hall

26-3 CnidariansWhat Is a Cnidarian?When a shrimp or smallfish brushes up againstthe tentacles, thousandsof nematocysts explode,releasing enough poisonto paralyze or kill theprey.Slide6 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansWhat two body plans exist in the cnidarianlife cycle?Slide7 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansForm and Function in CnidariansCnidarians are radially symmetrical. They have acentral mouth surrounded by numerous tentaclesthat extend outward from the body.Slide8 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansCnidarians typically have a life cycle thatincludes two different-looking stages: apolyp and a medusa.PolypMedusaSlide9 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansA polyp is a cylindricalbody with armliketentacles. In a polyp, themouth points upward.Polyps are usuallysessile.PolypSlide10 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansA medusa has a motile,bell-shaped body with themouth on the bottom.MedusaSlide11 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansCnidarian polyps and medusas each have a bodywall that surrounds an internal space called agastrovascular cavity.GastrovascularcavityGastrovascularcavitySlide12 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansThe gastroderm is the inner lining of thegastrovascular cavity, where digestion takes place.Gastrovascular cavityGastrovascular cavitySlide13 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansThe epidermis is the outer layer of cells.EpidermisEpidermisSlide14 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansThe mesoglea is a layer that lies between theepidermis and gastroderm.MesogleaSlide15 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansFeedingA cnidarian pulls its food through its mouth andinto its gastrovascular cavity, a digestivechamber with one opening.Food enters and wastes leave the body throughthat same opening.Slide16 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansThe digestion that occurs in the gastrovascular cavityis extracellular, meaning that it takes place outside ofcells.Partially digested food is absorbed by thegastroderm.Digestion is completed intracellularly, within cells inthe gastroderm.Any materials that cannot be digested are passed outof the body through the mouth.Slide17 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansRespiration, Circulation, and ExcretionFollowing digestion, nutrients are usuallytransported throughout the body by diffusion.Cnidarians respire and eliminate the wastes ofcellular metabolism by diffusion through their bodywalls.Slide18 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansResponseCnidarians gather information from theirenvironment using specialized sensory cells.Slide19 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansBoth polyps and medusashave a nerve net, aloosely organizednetwork of nerve cells.Nerve cellsSlide20 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansReproductionMost cnidarians reproduce both sexually andasexually.Polyps can reproduce asexually by budding.In most cnidarians, sexual reproduction takesplace with external fertilization. Externalfertilization takes place outside the female's body.Slide21 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansIn the life cycle of Aurelia, a common jellyfish, thefemale releases eggs into the water, and the malereleases sperm.Slide22 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansFertilization occurs in open water.Each zygote grows into a free-swimminglarva.Slide23 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansThe larva eventuallyattaches to a hardsurface and develops intoa polyp.Slide24 of 47Copyright Pearson Prentice Hall

26-3 CnidariansForm and Function in CnidariansThe polyp eventuallybuds and releases youngmedusas that begin thecycle again.Slide25 of 47Copyright Pearson Prentice Hall

26-3 CnidariansGroups of CnidariansWhat are the three groups of cnidarians?Slide26 of 47Copyright Pearson Prentice Hall

26-3 CnidariansGroups of CnidariansGroups of CnidariansCnidarians include:• jellyfishes• hydras and their relatives• sea anemones and coralsSlide27 of 47Copyright Pearson Prentice Hall

26-3 CnidariansGroups of CnidariansJellyfishesThe Class Scyphozoa contains the jellyfishes.Jellyfishes live their lives primarily as medusas.The polyp form of jellyfishes is restricted to a smalllarval stage, and no elaborate colonies ever form.Jellyfishes reproduce sexually.Slide28 of 47Copyright Pearson Prentice Hall

26-3 CnidariansGroups of CnidariansHydras and Their RelativesThe Class Hydrozoa contains hydras and relatedanimals.The polyps of most hydrozoans grow in branchingcolonies that can extend more than a meter.Within the colony, polyps are specialized toperform different functions.Slide29 of 47Copyright Pearson Prentice Hall

26-3 CnidariansGroups of CnidariansSea Anemones and CoralsThe Class Anthozoa contains sea anemones andcorals, animals that have only the polyp stage intheir life cycle.Anthozoans all have a central body surrounded bytentacles.Slide30 of 47Copyright Pearson Prentice Hall

26-3Continue to:- or -Click to Launch:Slide31 of 47Copyright Pearson Prentice Hall

26-3The characteristic that defines the cnidarians isa. bilateral symmetry.b. stinging cells.c. a gastrovascular cavity.d. cephalization.Slide32 of 47Copyright Pearson Prentice Hall

26-3Which of the following statements is generallytrue of polyps and medusas?a. Polyps are sessile, and medusas are motile.b. Polyps are motile, and medusas are sessile.c. Both polyps and medusas are sessile.d. Both polyps and medusas are motile.Slide33 of 47Copyright Pearson Prentice Hall

26-3During the life cycle of Aurelia, the zygote growsinto a free-swimminga. polyp.b. larva.c. medusa.d. gemmule.Slide34 of 47Copyright Pearson Prentice Hall